ABSTRACT Alcoholics Anonymous (AA) is now well-established in its capacity to help individuals recover from alcohol use disorder (AUD), but there are substantial gaps in understanding the mechanisms by which it does so. Recent studies suggest two novel domains of mechanisms: 1) decreases in impulsivity; and 2) increases in salutary social networks. However, these mechanisms have been investigated in only a small number of studies and the extant studies employed low resolution measurement and suboptimal study designs. The proposed study will address these limitations to systematically investigate impulsivity and social network composition as novel mechanisms of behavior change (MOBCs) for AA?s positive effects on AUD recovery. The first primary aim is to examine impulsivity, fractionating the concept into three distinct forms: 1) steep discounting of future rewards (i.e., delay discounting); 2) poor behavioral inhibition (i.e., inability to inhibit a prepotent response); and 3) impulsive personality traits (i.e., self-attributions about regulatory capacity). The second primary aim is to examine social network properties, quantifying participant social relationships via formal egocentric social network composition analysis. The third primary aim is to examine whether these mechanistic relationships systematically differ according to three important moderators: age, sex, and study site. An exploratory secondary aim is to mine the findings from the primary aims to generate specific recommendations and applications for clinical practice. These aims will be executed in a prospective cohort design that is optimized for characterizing lagged dynamic changes in MOBCs. Specifically, the study design will examine these processes in individuals with AUD who are newly engaging in community outpatient AUD treatment. Participants will receive assessments at baseline, 6-weeks, and 3-, 6-, 9- and 12-months. AA involvement will be measured using both the traditional measure of frequency of meeting attendance and a novel measure of AA program engagement. Outcome variables will include percent days abstinent and percent heavy drinking days. The findings will be disseminated using a comprehensive knowledge translation plan. Collectively, the proposed study has the potential to make major contributions to understanding how AA helps people recover from AUD. In turn, the insights from the study have the potential to substantially contribute to the use of AA and other mutual recovery services in clinical practice.